The present invention relates to a motor rotor and, more particularly, to a motor rotor including a metal ring providing a magnetically sealing effect for a magnet ring.
FIGS. 1 and 2 show a conventional motor rotor 4 including a hub 41 having a shaft 411 mounted to a center thereof, a metal ring 42 mounted to an inner periphery of a peripheral wall of the hub 41, and a magnet ring 43 mounted to an inner periphery of the metal ring 42. The metal ring 42 includes inverted L-shaped cross sections to provide reliable engagement with the hub 41. The metal ring 42 between the hub 41 and the magnet ring 43 provides a magnetically sealing effect for the magnet ring 43. However, formation of the metal ring 42 with inverted L-shaped cross sections requires several punching processes, leading to troublesome processing and waste of material. As a result, the manufacturing costs of the motor rotor 4 are increased while wasting material.
FIGS. 3 and 4 show another conventional motor rotor 5 including a hub 51, a metal ring 52, and a magnet ring 53. The metal ring 52 is formed by bending a strip of metal plate having a length equal to or slightly smaller than the inner periphery of the peripheral wall of the hub 51. The metal ring 52 is mounted to the inner periphery of the peripheral wall of the hub 51 and exerts a radially expanding force to and is thus in tight contact with the inner periphery of the peripheral wall of the hub 51. Two ends of the magnet ring 53 can be in contact with or spaced from each other. The magnet ring 53 is then tightly fitted onto the inner periphery of the metal ring 52. Such a motor rotor 5 is disclosed in U.S. Pat. No. 6,362,551 issued Mar. 26, 2002. Formation of the metal ring 52 by bending a strip of metal plate avoids waste of material while allowing easy manufacturing. However, the ends of the metal ring 52 are not positioned and, thus, liable to shift in the axial direction (see FIG. 4), leading to difficulty to subsequent assembly of the magnet ring 53 as well as an adverse affect to rotational stability of the rotor 5. assembly of the magnet ring 53 as well as adverse affect to rotational stability of the rotor 5.